Frequency converter selection to determine the following points.
1) the purpose of using frequency conversion; constant pressure control or constant current control, etc..
2) the type of load of the frequency converter; such as vane pumps or displacement pumps, etc., pay special attention to the performance curve of the load, the performance curve determines the application of the ways and means.
3) frequency converter and load matching problems.
I. Voltage matching; the rated voltage of the inverter and the rated voltage of the load in line.
II. Current matching; ordinary centrifugal pump, the rated current of the inverter and the rated current of the motor in line. For special loads such as deep water pumps need to refer to the motor performance parameters to determine the maximum current inverter current and overload capacity.
III. Torque matching; this situation is possible in constant torque load or when there is a deceleration device.
4) When using inverter to drive high speed motor, due to the small reactance of high speed motor, the increase of high harmonics leads to the increase of output current value. Therefore, the selection of inverter for high-speed motor, its capacity should be slightly larger than the selection of ordinary motor.
5) If the frequency converter is to be run on long cables, then measures should be taken to suppress the influence of long cables on the ground coupling capacitance, to avoid insufficient output power of the frequency converter, so in this case, the capacity of the frequency converter should be enlarged by one grade or output reactor should be installed on the output side of the frequency converter.
6) For some special applications, such as high temperature, high altitude, this will cause the inverter capacity reduction, inverter capacity to be enlarged a gear.
Selection strategy of inverter
1) Load purchase
The load driven by the motor is not the same, the requirements of the inverter are not the same.
A: fans and pumps are the most common loads: the most simple requirements of the inverter, as long as the inverter capacity is equal to the motor capacity can be (air compressors, deep-water pumps sediment pumps, rapid changes in the musical fountains need to increase capacity).
B: crane class load: this type of load is characterized by a large start-up impact, so the inverter is required to have a certain margin. At the same time, in the heavy lowering elbow, there will be energy feedback, so we should use the braking unit or use a common bus way.
C: uneven loads: some loads are sometimes light, sometimes heavy, this time should be in accordance with the heavy loads to choose the inverter capacity, such as steel mill machinery, crushing machinery, mixers, etc..
D: large inertia loads: such as centrifuges, punching machines, rotary kilns in cement factories, such loads are very large, so the start-up may oscillate, motor deceleration when there is energy feedback. A slightly larger capacity inverter should be used to speed up the startup and avoid oscillation. Combined with the brake unit to eliminate the feedback energy.
2) Production purchase
Users should purchase according to the specific conditions of the production machinery If it is an excavator, it should choose the high-function special inverter with torque control function, because this kind of inverter has large low-speed torque, static mechanical characteristics of the hardness is not afraid of the load impact, and it can improve the low-speed torque by increasing the capacity of the motor and the inverter; if it is to control the compressor, due to the complexity of the compressor's torque characteristics, especially starting torque, therefore, it should choose the torque characteristics of the compressor. If it is to control the compressor, due to the complexity of the compressor torque characteristics, especially the starting torque is very large, so it should choose the high performance vector inverter with good torque characteristics and current limiting function.
If it is to control the compressor, because the torque characteristic of the compressor is complicated, especially the starting torque is very large, so it should choose the high performance vector inverter with good torque characteristic and current limit function. If it is used for paper making and chemical fiber equipment, it should choose closed-loop vector inverter with high precision and high response characteristics.
3) Reliability purchase
According to the reliability of the purchase of inverters, the purpose of using inverters is to improve production efficiency, if the performance is good but the reliability is not good, often out of order, it is not worth the loss. China's vast territory, the southern region of the year-round high temperature and humidity, the coastal areas are mainly salt corrosion, these will cause equipment insulation decline, the northern climate is dry, easy to generate static electricity, large temperature differences between winter and summer, and each enterprise's production environment is very different, these factors are in the purchase of inverters should be considered. Some inverter performance is very good, but poor environmental adaptability, there may be frequent failures affect production.
4) Price selection
According to the price of the purchase of inverters, which is the main consideration in the purchase of inverters, but if the one-sided pursuit of low prices, often leads to a decline in quality and reliability, because the power devices in the inverter and the main loop electrolytic capacitors account for about 70% of the cost, some manufacturers in order to reduce costs, with a voltage of 1000 volts instead of 1200 volts module, with a current of 25A instead of 30A, with ordinary Low-frequency electrolytic capacitors instead of special high-frequency electrolytic capacitors for inverters, this kind of inverter will not be found to have any problems in normal conditions or short time use, but due to the reduction of the module's power margin, it will be easy to be damaged once it happens to be blocked by the motor, instantaneous high voltage of the power grid, and sustained high temperature.
5) Power purchase
According to the power module purchase inverter, now common inverter key device power module is IGBT module and IPM intelligent power module, especially IPM module, although the cost is higher, but because the module has an internal overcurrent, short-circuit, undervoltage, output ground, overheating and other protection functions, once anomalies occur, the module internal self-protection immediately, and then through external protection circuits for the second time to protect, the possibility of burning the module is greatly reduced. The possibility of burning the module is greatly reduced and the reliability is significantly improved. The use of GTR module products, due to the GTR itself has no protection function, external protection circuits and promote the complexity of the circuit, once the protection can not keep up, the module burned in an instant. Some manufacturers still use GTR modules in order to reduce costs, which is also a purchase of inverters need to pay attention to.
In the installation of the inverter should also pay attention to, the installation location must be cloud in line with the standard environmental requirements, otherwise it is easy to cause failure or shorten the service life; inverter and drive the distance between the motor is generally no more than 50 meters, if you need a longer distance you need to reduce the carrier frequency or increase the output reactor options to normal operation.
Finally, to choose to select a manufacturer or distributor with good technical strength and after-sales service, and then good products have the possibility of failure, only with good technical strength of the manufacturer or distributor, you can get thoughtful technical service, free from worries.